Ellipsometer nulling: coupling and setting uncertainty.

During the nulling of an ellipsometer, coupling is experienced between its adjustable components. In this paper a criterion for coupling is reported, which is useful from a practical point of view. The criterion has been applied to known cases in generalized and conventional ellipsometry. The influence of coupling and detector sensitivity on the setting uncertainty of the adjustable components has been studied. A discussion of the choice of the nulling scheme has been included.